Lift-trucks are widely used for loading, lifting, handling and carriage of heavy loads, such as large containers and cars. Typically, a designated lifting-vehicle comprises an built-in fork lift mechanism, which is preferred over elaborate crane lifts. Relatively light weights can be loaded in front or back of non-designated vehicles, without significantly endangering the stability of the lifting-vehicle. However, heavy loads must be loaded in proximity to the center of gravity in order to avoid turning over of the lifting-vehicle during the loading and unloading process, especially while the lifting-vehicle is in motion. Hence, conventional fork lift trucks comprise a designated truck having a fork lift mounted in front thereof, with a balancing counterweight mounted in the rear of the truck. In certain cases the mast of the fork lift is tilted in order to maintain the center of gravity.
Still, for some purposes, such as for towing cars and other vehicles, it is preferable to use a retractable fork lift mechanism which is mounted on the side (or rear) of the lifting-vehicle. In the latter cases, when the vehicle is in motion, the prongs of the fork overlappingly rest over the lifting-vehicle's frame, with or without cargo. During the process of loading and unloading, the prongs extend from the frame of the vehicle and lift the cargo--from underneath, in a combined downward-upward and traversing motions. The prongs are situated during this process anywhere between the ground and at some elevation above the chassis of the lifting-vehicle. To enable these combined motions, the chassis of the lifting-vehicle is designed as an open, II shaped rectangle, whereby the prongs reciprocate through the open side of the chassis.
In the latter cases, the open side of the chassis is usually located at the side of the lifting-vehicle--as required, for example, for loading and towing away cars which are unlawfully parked along the sides of a street. In such embodiments most of the weight of the lifting-vehicle itself is predisposed at the side of the lifting vehicle. This results from the accumulation of the necessary lifting equipment on the closed side of the II-shaped chassis. Although such accumulation contributes to counter-balance the weight of the loaded cargo, it is disadvantageous when there is no cargo loaded or when the loaded cargo is relatively lightweight.
The above embodiment entails several further disadvantages: The requirement of a II-shaped chassis necessary for the task of side loading, excludes the possibility of using conventional trucks and trailers having a "closed" chassis.
In addition, due to the unbalanced lack of a support beam in the open side of the II-shaped chassis, the strength of the chassis is disproportional reduced, even when the other support beams are reinforced, and especially when the chassis lacks a longitudinal support beam. Such weakened chassis is therefore suitable for transportation via regular roads and highways and the use of such lift trucks is usually restricted to special loading zones.
Moreover, the II-shaped chassis poses a serious obstacle for the power transmission from the engine, mounted on one side of the loading vehicle, to the wheels which are mounted on the other side of the vehicle. Similar problems arise with regard to the brake system and the shock-absorbers and even the very engagement of the wheels to the chassis is problematic with the II-shaped chassis.
In view of the above constructural restraints of such lift-trucks, which are designed for lifting a heavy load from their side, they comprise a hydraulic power source which serves both the motion of the vehicle on the ground and the operation of the lifting mechanism. Therefore, their speed on regular roads must be further restricted due to the hydraulic power source which is inferior to regular combustion engines.
Furthermore, some conventional fork lifts carry the load on the prongs while the lift-truck is in motion, a method which is unsafe and may damaging to the load.
Finally, the II-shaped chassis is restricted to lifting loads from one side only of the lifting vehicle, a restriction which can be a major disadvantage. Such is the case, for instance, of a lifting truck used for towing-away cars which are unlawfully parked on both sides of a narrow street. When the lifting-truck is confined to drive in one direction only, the lifting of cars is possible only on one side of the road.
It is therefore, an object of this invention, to provide novel fork lift adapted to the loading of light and heavy loads on the side of the fork lift, which overcomes the above disadvantages.
In particular, an object of this invention is to provide a fork lift which can be mounted on conventional chassis of a vehicle, such as conventional trucks or trailers, and which can be dismounted therefrom.
Another object of this invention is to provide a fork lift which will enable the lifting vehicle to move fast and safely in roads and highways, using a safe chassis and enabling the use of combustion engine for the drive of the vehicle.
A further particular object of this invention, is to provide a fork lift which can be used for lifting loads from either side of the lifting vehicle.
Yet, a further object of this invention is to provide a fork lift wherein the loaded cargo can be safely supported - and is not carried by the prongs of the fork lift while the vehicle is in motion.
These and other objectives are provided by the invention to be described below.